The Arizona sentinel., 1887-05-21
HOW CREAM RISES.
Many Points That Are But Imperfectly
 Understood by Most Dairymen.

The secret Ol IdlSIllS CISdA COioiSlo in suddenly cooling the milk. In round numbers we are told that milk is eighty-seven per cent water, four per cent. sugar, and the same quantity of butter fats. The fat is the part which we wish to separate from the milk, to manufacture into butter. Milk is a little heavier than water, probably on account of the sugar it contains. It also heats and cools much slower than water, hence it is what our scientific friends call "bad con- ductor."
 If milk, which is composed so large. ly of water heats and cools more slowly than water, it can only be ac- counted for by the fact that the re- maining thirteen per cent, which con. tains the butter fat, holds heat, or keeps the milk from cooling as soon as water, under pre- ciselv similar conditions. We know that milk or water will shrink in cool ing, at least we know that the power of steam is due to the expansion of water caused by heat. I find that milk contracts so it weighs about half an ounce more to the gallon at forty-eight degrees than at ninety-eight degrees.
 To prove this last statement that water is a better conductor of heat than milk, put one hand into pail of water at temperature of thirty-two degrees, and hold the other in pail ot milk, of the same temperature. You will find that the hand in the water will feel a sensation of cold before the one in the milk.
 Take can of milk eight and hali inches in diameter, and twenty inches deep. Place this in vessel of water of the same depth, which contains as much water as the other does of milk. The temperature of the milk being ninety-eight degrees, and of the water forty-eight degrees. In a short time the thermometer will show us that the milk and the water are both of the same temper ature, or seventy-three degrees, the water having taken part of the heat from the milk, thereby increasing it's own temperature, and decreasing that of the milk. If a can of milk were placed in large quantity of water, as in a well, there would be so much more water than milk that the milk would be reduced to the temperature of the water without sensibly decreasing the temperature of the water. It would be found that the temperature of the milk had not only been decreased, but that the cream had risen to the surface, ii the milk had been left long enough in the water. Why? Water on cooling shrinks, and becomes denser-that is, weighs more, cubic foot for foot. Now, when the milk is placed in the cold water it is gradually cooled. but it does not cool evenly. As said before, eighty-seven per cent. of the milk is water, and this cools more rapidly than the other thirteen per cent. of fats, etc, and consequently shrinks and becomes heavier. If we put two liquids in a vessel together, the heavier one will sink to the bottom, and the lighter one rise to the top just so the watery part of the milk set ties to the bottom of the can, and the lighter part, which does not cool Sc rapidly as the water, and therefore shrinks slower, rises to the top. If this reasoning is true, it is very important that it be well understood, so that the underlying principle may be taken ad- vantage of by the different farmer: whose conveniences for their work vary so widely.
 There is one point which must not be overlooked in the above reasoning. We have said that cooling milk causes it to shrink and become heavier, but the temperature must never be below thirty-nine degrees. If have not for gotten the valuable lesson that water shrinks as it cools to thirty-nine de grees, and then begins to expand i cooled further. Cooling below thirty. nine degrees is, therefore, detrimental
 I have made this study many years and came to the conclusion here giveT long ago, and acted upon it. This study has been to perfect the system of cream raising that can be done on tht farm. One that the farm provides for the year round without even th' aid of ice, though ice is valuable hell in hot weather The temperature ot deep wells is about forty-eight, anC this will answer very satisfactorily for cream raising, provided we do not de lay in straining and setting the cans in this well water, and do not allow the water to warm up, which it vii surely do if there is not large enougl quantity of it, or if it is not oftel changed. The water will conduct tht heat out of the milk into itself just a surely as it will conduct the heat ou of red-hot iron placed in it.-F c Curtis, trs PrGirie Farmer.
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